Empirical Assessment of Effect of Publication Bias on a Meta-Analysis of Validity Studies on University Matriculation

This study examined the impact of publication bias on a meta-analysis of empirical studies on validity of University Matriculation Examinations in Nigeria with a view to determine the level of difference between published and unpublished articles. Specifically, the design was an ex-post facto, a causal comparative design. The sample size consisted of 30 empirical studies selected on the basis of empirical status and relevance. The characteristics of these studies were recorded, coded and analyzed. The results revealed that the impact of publication bias was minimal on the meta-analysis study since the two versions i.e. published and unpublished articles yielded essentially similar estimates of effect sizes. (Mean Fisher =0.393, Weighted Fisher =0.398 with associated r =0.375 for both). Even though the use of non- representative proportion of significant studies in the two positive directions led to a non-representative set of studies, published articles had a higher effect size than the unpublished articles. ( = 0.460 for published, while =0.279 for unpublished). The effect size of published articles was significantly different from unpublished articles ( χ2=5.42 p < 0.05 sig). This was an indication that studies with more significant results were the published. On the overall, there was no significant difference in the level of significance for both published and unpublished articles ( χ2 = 0.0031 p > 0.05). Hence, publication bias did not affect the results of this meta-analysis.